Homogeneous transition metal catalyzed reactions have been refined into important processes for the synthesis of high-valued organic compounds (a) G. W. Parshall, S. D. Ittel, Homogeneous Catalysis: The Application and Chemistry by Soluble Transition Metal Complexes, Wiley VCH, 1992; b) F. Diederich, P. J. Stang Metal Catalyzed Cross-Coupling Reactions; Wiley-VCH: Weinheim 1998. c) M. Beller, C. Bolm, Transition Metals for Organic Synthesis; Wiley-VCH: Weinheim 1998). From these, Palladium-catalyzed cross-coupling reactions have emerged as one of the most important reactions both in industry and academia. In recent years there have been numerous contributions in this area (a) J. Tsuji, Palladium Reagents and Catalysts: Innovations in Organic Synthesis; Wiley: Chicester, 1995.).
Palladium catalysts bearing an N-heterocyclic carbene and sterically demanding phosphine ligands display the most robust and active catalytic systems to date (review on Pd-complexes of N-heterocyclic carbenes for cross-coupling reactions: M. G. Organ et al. Angew. Chem. Int. Ed. 2007, Vol 46, 16, 2768-2813, recent examples of applications of phosphine ligands: M. Beller, Adv. Synth. Catal. 2008, 350, 2437-2442, M. Beller, Chem.—Eur. J. 2008, 14, 3645-3652; S. L. Buchwald Acc. Chem. Res. 2008, Vol. 41, 11, 1461-1473 and references cited therein).
However, the application of homogeneous transition metal catalysts can result in soluble metal contamination. These soluble metals can be detrimental to product quality and product yield. In the case of active pharmaceutical ingredient (API) development, the metal catalyst must be removed to a regulated level. This can be achieved by e.g. chemical metal scavenging substances or techniques where the metal residues are removed by physical methods such as extraction, distillation or precipitation.
From the industrial point of view one attractive physical method constitutes membrane filtration technology in which the organic materials are removed by filtration and the metal catalyst remains within the membrane sphere.
Methods for removing the catalyst by either chemical or physical methods are usually very complex and thus expensive or in the case of membrane filtration can't be employed because there are no membranes available with the required selectivity.
It is thus an object of the present invention to provide ligands and/or their salts as well as metal complexes comprising said ligands for homogeneous catalysed reactions with which the disadvantages of the prior art are at least reduced and that allow simple and cost efficient separation of metal complexes and reaction solution.
This object is achieved with polyhedral oligomeric silsesquioxanes (POSS)-linked ligands according to general formula I and the corresponding salts according to general formula II as well as bidentate polyhedral oligomeric silsesquioxanes (POSS) linked ligands according to general formula III and the corresponding salts according to general formula IV.
The POSS linked ligands according to the invention thus do not necessarily have to be monodentate. They could also be used as bidentate or tridentate ligands which are connected by linker molecules e.g. alkyl chains. The POSS linked ligands in a bidentate or tridentate molecule can be identical or different from each other.
Since for the production of metal complexes often the salts of the ligands are used the invention also encompasses the salts of the POSS linked ligands. Said salts are obtained by the simple reaction of a leaving group containing POSS-connected alkyl residue with the corresponding ligand. The leaving group may e.g. be halogen, sulfonate, triflate, acetate or phosphate.

in which (R1a,b,c)n-1(SiO1,5)n is a polyhedral oligomeric silsesquioxane (POSS) with n=4, 6, 8, 10, 12, 14, 16 or 18 and
R1a, R1b, R1c is each independently selected from the group consisting of same or different branched or linear C1-C20 alkyl chains, cyclo alkyl, C1-C20 alkoxy, aryl, aryloxy, heteroaryl and arylalkyl groups,
k, l, m is 0 or 1 provided that k+l+m≧1,
R2a, R2b, R2c is a spacer that binds the polyhedral oligomeric silsesquioxane (POSS) to the ligand L,
R2a, R2b, R2c is each independently selected from the group consisting of linear or branched C1-C20 alkyl, C3-C10 cyclic alkyl, C1-C20 alkoxy, C2-C20 alkenyl, C2-C20 alkenyloxy, aryloxy, C1-C20 alkylthio, C1-C20 carboxylate, aryl or heteroaryl, C1-C20 alkyl halogenide, annulated aryl or heteroaryl, C3-C10 cyclic alkyl groups which in turn may each be further substituted with one or more groups selected from hetero atom or aryl groups, ether, polyether polythioether, amino, aryl bridged alkyl chain where the aryl moiety can include further substitution pattern and
in structures I and III ligand L is an uncharged electron donor, whereas in structures II and IV L+ is a protonated species of L,
H is hydrogen,
Q is a branched or linear substituted or unsubstituted alkyl chain with a chain length ranging from C1 to C20. Furthermore Q may be a unsubstituted or substituted cyclic alkyl, aryl or heteroaryl group where the aryl and heteroaryl moieties can include further substitution pattern.
X− is a mono- or polyvalent organic or inorganic anion
The phrase “polyhedral oligomeric silsesquioxanes (POSS)” as used herein means that the POSS molecule can be regarded in a simplified manner as a roughly 3-dimensional geometric structure with flat faces and straight edges in which the Si-atoms are located at the corners of the structure.
For example for n=6 the POSS molecule is a pentahedral structure in the shape of a triangular prism with 6 Si atoms located at the corners of the structure.

In another example with n=8 the POSS molecule is a hexahedral structure in the shape of a cube with 8 Si atoms located at the corners of the structure. It should be noted that substituents R in the structure shown above and in the following structures are not all identical. One substituent R is needed as spacer that binds the POSS molecule to the ligand L, i.e. one of the substituents R equals substituent R2.

For n=10 the POSS molecule is a heptahedral structure in the shape of a pentagonal prism with 10 Si atoms located at the corners of the structure.

POSS molecules are known to the skilled artisan since the first synthesis by Lichtenhan et al. in 1995 (J. D. Lichtenhan Comments. Inorg. Chem. 1995, Vol. 17, No. 2, pp. 115-130; A. M. Seifalian, Acc. Chem. Res. 2005, Vol 38, No. 11 879-884). The POSS molecules which are also referred to as POSS-cages display rigid and robust structures due to the strong framework resulting from their shorter bond.
The spacer R2a, R2b, R2c bonds to the polyhedral oligomeric silsesquioxanes (POSS) molecule over a Si or O atom of the POSS molecule. The spacer R2a, R2b, R2c can bond to the ligand L via all bonds that are known to the skilled artisan preferably via C, O, N or S:

Surprisingly it was found that polyhedral oligomeric silsesquioxanes (POSS) molecules with the generic formula ((R1)n-1(SiO1,5)n R2) can be bonded to ligands and thus be used for enlarging the catalyst structure in order to enable membrane filtration separation. R1, R2 is a generic term that also includes the a, b, c species as previously defined. One drawback of mass dependent membrane-filtration methodology is that a certain mass difference between the used catalyst and the substrates (and products) is required, so that retention of the catalyst is possible while product is transported through the membrane. Thus, most filtration techniques are limited to small sized molecules with a much lower molecular mass than the catalyst, since commercially used catalysts are of molecular weight between 400 and 900 g/mol.
As a solution to this problem, POSS-enlarged ligands for homogeneous catalyst systems are presented in this invention. These catalysts preferably have molecular weights ranging from 1500 to 3000 g/mol. Due to the increased mass of the catalyst a mass difference between catalyst and product can be reached that is sufficient to separate catalyst and product by membrane filtration. Products of a much larger weight range can thus be separated from a homogeneous catalyst comprising POSS enlarged ligands. The increased mass allows retention of the catalyst, passage of the product and final isolation of larger molecules by filtration. With respect to the production processes of intermediates and final products for the pharmaceutical industry, these new catalyst systems are of high-interest.
In the context of the present invention ligands are chemical compounds comprising one or several atoms. A coordinate bond is formed when one or several atoms of a ligand contribute their electrons or their orbitals filled with electrons to another atom. The ligand contributing the electrons is designated as the “donor” whereas the atom accepting the free electrons or the electrons from a filled orbital of the donor is designated as the “acceptor”. Ligand-atoms contributing the electrons or orbitals for the coordinate bonds, usually, are main-group-elements from groups III-VII with low oxidation numbers (e.g. C, N) Acceptors on the other hand, typically, are metal atoms with high oxidation numbers, e.g. z. B. Pd(II), Ru(III). An uncharged donor, thus, is a ligand without net-charge that contributes electrons or orbitals filled with electrons for a coordinate bond with an acceptor. Examples of uncharged donors are (wherein the two dots preceeding the letter depict the electrons participating in the coordinate bond):
PH3P:, R2N:, Ph3As:, or:

Importantly, carbon too can act as an uncharged (electron) donor. Mostly found as carbene, the carbon atom bears a pair of electrons in an orbital. These electrons are provided for an uncharged sigma bond with the metal center. This is usually expressed by structures drawn as:

Charged (electron) donors on the other hand carry a net-charge, i.e. cationic donors bear a positive net-charge and anionic donors bear a negative net-charge.
The polyhedral oligomeric silsesquioxane (POSS)-linked ligands and their salts according to the invention can be considered as “nanoparticles or nanocomposites” due to the fact that their size ranges several nanometers.
Even more surprisingly the POSS linked ligands and their salts according to the present invention are on the one hand soluble which is a precondition for their use in homogeneous catalysis and on the other hand filtratable by membrane filtration methods which is a precondition for their cost efficient and simple removal out of a reaction solution. The use of POSS linked ligands or their salts for homogeneous transition metal catalysts therefore combine in an unexpected manner the advantages of homogeneous catalysis, i.e. high accessibility and high activity with the advantage of a simple removal of the catalyst. The POSS linked ligands or their salts therefore allow for the first time the use of homogeneous transition metal catalysts for continuous processes.
The POSS linked ligands in particular their salts have another advantage over ligands or their salts that are not linked to a POSS molecule. Ligand salts having very low solubility in common organic solvents e.g. toluene show significantly improved solubility when they are linked to a POSS molecule. Compared to imidazolium or phosphonium salts which are used for the construction of transition metal catalysts in homogeneous processes, POSS enlarged salts thereof show drastically enhanced solubilities. The enhanced solubility will greatly facilitate the construction of the transition metal catalysts with these ligand salts in terms of ease of reaction performance. Tests showed that in toluene, which is widely used as solvent in commercial applications, POSS-free imidazolium and phosphonium salts are unsoluble whereas the POSS-derivatives can be dissolved very well.
In preferred embodiments the present invention also pertains the application of novel nanoparticle linked phosphine and N-heterocyclic carbene ligands in cross-coupling reactions, where nanometer sized polysilsesquioxane cubes or other polyhedral shapes as mentioned above serve as nano-anchors.
Preferred substituents R1a, R1b, R1c of the polyhedral oligomeric silsesquioxanes (POSS) linked ligands according to the invention are unsubstituted branched alkyl chains. These substituents ensure solubility of the POSS architecture in various organic polar and non-polar solvents. It is thus important that the preferred substituents R1a-c bear no functional groups such as e.g. OH, NH or COOH. Otherwise chemical interaction between these functional groups and the catalyst or other reagents that are employed within the application could result especially when L is a N-heterocyclic carbene. Finally the said POSS-substituents contribute to further enlargement of the POSS-moiety.
In another preferred embodiment of the invention the spacer molecules R2a, R2b, R2c are linear C1-C20 alkyl, more preferably linear C3-C10 alkyl.
In yet another preferred the polyhedral oligomeric silsesquioxanes (POSS) ligands are of the general formula (II)L[(R1a)n-1(SiO1,5)nR2a]k  (II)
in which R1a, n, R2a have the same meaning as described above and k=1.
The ligand L is preferably selected from the group consisting of N-heterocyclic carbene, amine, imine, phosphine, stibine, arsine, carbonyl compound, carboxyl compound, nitrile, alcohol, ether, thiol or thioether.
More preferably ligand L of the polyhedral oligomeric silsesquioxanes (POSS) ligand according to the invention is a N-heterocyclic carbene. N-heterocyclic carbenes are extremely reactive intermediates that are very difficult to isolate. Further, many substances destroy the N-heterocyclic carbenes through chemical interaction. It is thus surprising that it is possible to link the oligomeric silsesquioxanes (POSS) molecules with a N-heterocyclic carbene ligand.
Most preferably the polyhedral oligomeric silsesquioxanes (POSS) linked N-heterocyclic carbenes or their salts are of the following structures:

Additionally preferred are polyhedral oligomeric silsesquioxanes (POSS) linked triazole-carbenes or their salts that are of the following structures:

wherein:
R1 is the same or different branched or linear C1-C20 alkyl chains, cyclo alkyl, C1-C20 alkoxy, aryl, aryloxy, arylalkyl groups, substitution pattern also includes further POSS fragments having the same or different structure. R1 may also be multiply substituted halogen alkyl, unsubstituted or substituted aryl groups and substituted alkyl groups, aryloxy, hetaryloxy groups.
X− is a mono or polyvalent organic or inorganic anion.
The spacer molecule R2 that binds the POSS-molecule and to the N-atom of the N-heterocyclic carbene is selected from the group consisting of C1-C20 linear or branched alkyl chain, ether, polyether polythioether, amino, aryl bridged alkyl chain where the aryl moiety can include further substitution pattern, C3-C10 cyclic alkyl, C1-C20 alkoxy, C2-C20 alkenyl, C2-C20 alkenyloxy, aryloxy, C1-C20 alkylthio, C1-C20 carboxylate, aryl or heteroaryl, C1-C20 alkyl halogenide, annulated aryl or heteroaryl, C3-C10 cyclic alkyl groups which in turn may each be further substituted with one or more groups selected from hetero atom or aryl groups. Additionally the alkyl chain can contain further complexing moieties like phosphine derivatives.
j is preferably 1-5 giving ring sizes of the heterocyclic ligand ranging from 5 to 8. In case of j=1 the most preferred heterocyclic ring moiety is imidazole. In case that j is 2, 3, 4 or 5 the additional substituents have the same meaning as R3, R4, R5 and R6.
R3, R4, R5 and R6 are the same or independent from each other and selected from the group consisting of hydrogen, linear or branched C1-C20 alkyl, C3-C10 cyclic alkyl, C1-C20 alkoxy, C2-C20 alkenyl, C2-C20 alkenyloxy, aryloxy, C1-C20 alkylthio, C1-C20 carboxylate, aryl or heteroaryl, multiply substituted halogen aryl or heteroaryl, C1-C20 alkyl halogenide, multiply substituted halogen alkyl, annulated aryl or heteroaryl, C3-C10 cyclic alkyl groups which in turn may each be further substituted with one or more groups selected from hetero atom or aryl groups.
In addition, R5 or R6 may also depict a POSS-molecule with the structure (R1)n-1(SiO1,5)n linked by a spacer molecule R2 to a carbon atom of the N-heterocyclic carbenes or their salts of the above given structures.
Preferably the N-heterocyclic carbene contains an additional C1-C20 alkyl chain-bridged POSS-moiety leading to a N-heterocyclic carbene ligand with two POSS molecules of the structure as depicted in formula VII and VIIa:

R2 is preferably an alkyl chain. Both R2 alkyl chain lengths can be independently or the same where both R2 enclose branched and linear C1-C20 (n=1-20) alkyl chains.
Additionally the POSS linked N-heterocyclic carbene may be connected via an alkyl chain R7 to another POSS linked N-heterocyclic carbene, e.g. POSS linked imidazole thus leading to a dimeric structure as depicted in formula VIII and VIIIa:

Wherein R7 is substituted or unsubstituted linear or branched C1-C10 alkyl chain.
Moreover, any of the ligands substituents R3-R6 may further include one or more functional groups. Examples of suitable functional groups include but are not limited to: hydroxyl, amine, amide, nitrile, thiol, thioether, ketone, aldehyde, ester, ether, imine, nitro, carboxylic acid, disulfide, carbonate and halogen.
Further preferred embodiments include the following structures:

Unsymmetrical substituted N-heterocyclic carbenes and the corresponding salts thereof contain one C1-C20 alkyl chain-bridged POSS-moiety on one N-atom and a 2,4,6-trimethylbenzene (mesityl) substituent on the other N-atom of the imidazole moiety (formulas IX and IXa).
Preferred embodiments of POSS linked triazole ligands are of following structures:

In another preferred embodiment of the polyhedral oligomeric silsesquioxanes (POSS) linked ligands according to the invention ligand L is a phosphine or a salt thereof.
The phosphine-based ligands or their salts disclosed in this present patent are preferably of general formula:

wherein:
R1 is the same or different branched or linear C1-C20 alkyl chains, cyclo alkyl, C1-C20 alkoxy, aryl, aryloxy, arylalkyl groups, substitution pattern also includes further POSS fragments having the same or different structure. R1 may also be multiply substituted halogen alkyl, unsubstituted or substituted aryl groups and substituted alkyl groups, aryloxy, hetaryloxy groups.
X− is a mono- or polyvalent organic or halide anionic ion.
R8 and R9 are the same or different branched or linear C1-C20 alkyl chains, cyclo alkyl, C1-C20 alkoxy, aryl, aryloxy, arylalkyl groups.
Most preferably R8 and R9 are adamantyl radicals XI or XIa where the phosphorus atom in XI is bound at the 2-position and in XIa at the 1-position.

The spacer R2 between the POSS-molecule and the attached phosphorus is selected from the group consisting of C1-C20 linear or branched alkyl chain, ether, polyether polythioether, amino, aryl bridged alkyl chain where the aryl moiety can include further substitution pattern.
In another preferred embodiment R2, R8 and R9 contain aryl groups, where the aryl groups are bonded to the P-atom and the POSS moieties is attached via alkyl chains R10 that are connected to the said aryl groups as depicted in formula XII. Alkyl chain R10 connected to the aryl group thus corresponds to spacer R2.

wherein:
R10 is the same or different branched or linear C1-C20 alkyl chains, cyclo alkyl, C1-C20 alkoxy, aryl, aryloxy, arylalkyl groups, substitution pattern also includes further POSS fragments having the same or different structure. R10 may also be multiply substituted halogen alkyl, unsubstituted or substituted aryl groups and substituted alkyl groups, aryloxy, hetaryloxy groups.
Additionally the alkyl chain can contain further complexing moieties like imidazol derivatives (formula XII):

Due to their size the POSS linked ligands according to the present invention can be considered as being nanoparticle anchored ligands. They can be used in metal catalyzed reactions in combination with nanofiltration technology. The nanometer-sized POSS-molecule to which the catalyst is linked allows specific filtration of the reaction products and other components where the nano-anchored catalyst remains within the membrane sphere. Most importantly high molecular weights of these ligands lead to the corresponding transition metal catalysts with molecular weights ranging from 1500 to 3000, which allows synthesis and filtration of larger sized molecules.
This methodology allows not only simplified separation of the metal catalyst from the organic components. Furthermore repeated multicycled processes and of course continuous processes are feasible as well.
Preferred examples of transition metal complexes with different POSS linked ligands are given below:

The corresponding transition metal complexes, preferably palladium complexes can be obtained and used in cross-coupling reactions in two ways: 1. they can be isolated after reaction of the phosphonium or imidazolium salts with bases and subsequent addition of a particular palladium source or 2. the active catalyst species can be obtained in the reaction mixture containing both catalyst compounds and the cross-coupling reaction partners in situ during the cross-coupling reaction in which a base is used in order to e.g. activate the palladium precatalyst or generate the active boronate species e.g. in the Suzuki-Miyaura reaction which is essential for the reaction.
Exemplary Synthesis of POSS-Linked Phosphine Ligands and or their Salts
Since most alkyl substituted free phosphines are prone to oxidation when exposed to air, it is far better to store these compounds as their phosphonium salts. The phosphonium salts are very stable compounds to moisture and air that can be stored for a very long time. The syntheses of the ligand salts are straightforward by simple reactions of polysilsesquioxane halides and the corresponding imidazole- and phosphine substrates.
The POSS linked phosphonium salts can be obtained by simple conversion of different POSS-halides having different chain lengths (scheme 1) with a phosphine. In this particular example the preferred bisadamantyl substituted phosphine is used since this phosphine substitution pattern is found in benchmark cataCXiumA®, which has proven to be a superior ligand in particularly manifold palladium-catalyzed cross-coupling reactions. Connecting the POSS cube with bisadamantylphosphine via an unbranched alkyl chain leads to a ligand structure which is very close to that found in cataCXiumA®.

This straight forward synthesis enables simple variation in both chain length between the phosphorus atom and the POSS cube and the moieties on the P-atom.
Exemplary Synthesis of Imidazole-Based NHC-Ligands or their Salts
From the group of imidazole-based NHC-type ligands the salts can be obtained simple reactions starting from POSS-halides and corresponding imidazole (scheme 2, left). For the synthesis of singly imidazole substituted POSS-derivatives, the POSS halides were added slowly two a melt of 10-30 fold excess of imidazol. Simple take-up of the crude product in water and extraction with ether gave the products in excellent yields and high purity.
The syntheses of symmetrically bis-POSS functionalized imidazolium salts were achieved by slight modification of the methodology as demonstrated for the syntheses of mono POSS-substituted imidazoles. The reaction of only two equivalents of imidazole with POSS alkyl halides lead to the clean formation of the corresponding imidazolium salts (scheme 2, right). Addition of at least two equivalents of imidazole is required, because the acid HX which results from the first reaction of one equivalent of imidazole needs to be buffered, otherwise incomplete reaction can occur. Finally, unsymmetrical mesityl-substituted POSS-enlarged imidazolium salts as N-heterocyclic carbene sources can be obtained by the simple protocol as well (scheme 2, top).

With the mono POSS enlarged imidazoles (from scheme 2) in hands, syntheses of various ligands that bear further POSS-substituted imidazole moieties or even mixed phosphine-NHC ligands were realized. Thus, starting from the mono POSS-substituted imidazole derivatives, in the first step the alkyl bridging moiety was installed (scheme 3, left). To avoid formation of side products, first an excess of the alkylating reagent (1,2-dibromoethane, 1,3-dibromopropane) was heated to 120° C. and the corresponding POSS-substituted imidazole derivative was added portionwise giving rise to the imidazolium salts.
On the other hand addition of 0.5 eq. of the alkylating reagent to the molten POSS-substituted imidazole derivative lead to the formation of the alkyl bridged dimer in very good yields (scheme 3, right).

The mixed phosphine-imidazolium-based NHC type of ligands are obtained by conversion of the POSS-containing singly alkylated imidazolium salts by treating with phosphines or their mineral salts respectively:

The symmetric POSS-substituted bis-imidazolium salts can be converted into the corresponding bis-NHC-transition metal complexes by treatment with a base and subsequent addition of an appropriate metal source. As an interesting candidate for general industrial application, Palladium was taken as metal of choice for the synthesis of various carbene- and phosphine complexes and their employment in C—C- and C—N-coupling reactions.
Furthermore new efficient and straightforward synthesis methods were established for the manufacture of these ligands to design new transition metal catalysts.